Magnetically actuated limit switch



Jan. 13, 1970 R. P. ALLEY 3,489,971

MAGNETICALLY ACTUA'PED LIMIT SWITCH Filed Oct. 6, 1967 lNVENTOR RoemrfiALLev BY W(A2MO ATTORNEY United States Patent Ice 3,489,971 MAGNETICALLY ACTUATED LIMIT SWITCH Robert Philbrick Alley, Danville, Ill., assignor to General Electric Company, a corporation of New York Filed Oct. 6, 1967, Ser. No. 673,413 Int. Cl. H01h 9/00 US. Cl. 335207 17 Claims ABSTRACT OF THE DISCLOSURE A magnetically actuated limit switch for indicating the relative movement or position of two objects. A magnetically actuable reed switch mounted on a first object is actuated by a magnetic field emanating from and terminating in magnetic members mounted on a second object so as to indicate the relative movement or position of the objects.

BACKGROUND OF THE INVENTION Many applications exist where it is desirable to indicate by the opening or closing of an electrical circuit the relative movement of two bodies. Typical of such applications are, detecting the position of a door, detecting movement of objects on a conveyor belt, detecting rotation of shafts, and many others. To detect such relative motion or movement many varieties of switches and switch actuating mechanisms have been utilized. These switches are fre quently called limit switches in that they operate as an automatic control to prevent a mechanism or process from going beyond a preset limit. The most common limit switches include a snap-type switch which is actuated by an arm pivoted on the snap switch housing. The arm in turn is engaged by an object or an extension thereof moving relative to the arm to trip the snap switch.

Where it has been desired to sense the position of a shaft, cams have been provided on the periphery of the shaft to engage a limit switch arm and thereby actuate a snap switch included in the limit switch. In such a typical arrangement the snap switch is of course subject to failure but, also the periodic engagement and disengagement of the arm and cam will cause wear of one or the other or both and failure to operate or improper operation of the limit switch will result.

OBJECTS OF THE INVENTION It is therefore a primary object of this invention to provide a novel and improved magnetically actuated limit switch which is of inexpensive and compact construction and which includes no moving elements subject to mechanical wear other than the electrical contacts.

It is another object of this invention to provide a novel and improved magnetically actuated limit switch which includes a highly reliable and long lasting sealed magnetic reed switch.

SUMMARY OF THE INVENTION These objects are accomplished in accordance with this invention, in one form thereof by providing a magnetically actuated limit switch for detecting relative positions of a pair of objects. The magnetically actuated limit switch includes a pair of magnetic members with magnetic poles formed therein, adjustably mounted with respect to each other on the first object, and also includes a magnetically actuated switch mounted on the second object such that in certain predetermined relative positions of the objects a properly oriented magnetic field extending between unlike magnetic poles on the two magnetic members passes through and thereby actuates the switch.

Other objects and further details of that which is be- Patented Jan. 13, 1970 lieved to be novel in the invention will be clear from the following description and claims taken with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of a rotating limit switch constructed in accordance with this invention;

FIGURE 2 is an enlarged side view of the rotating limit switch shown in FIGURE 1, with the shaft rotated from the position shown in FIGURE 1, and with portions shown in section and other portions broken away to show further details.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIGURES 1 and 2 of the drawing, a preferred embodiment of the magnetically actuated limit switch of this invention utilized to detect angular position and/ or rotary motion of a shaft 10 will be described. The basic elements of the magnetically actuated limit switch are a magnetically actuated switch 12 fixedly mounted near the shaft and a pair of magnetic members 14 and 16 mounted on the shaft 10 proximate to the switch 12 wherein a magnetic field extending between the magnetic members passes through the switch 12 and is effective to actuate the switch 12 in a certain range of predetermined positions of the shaft 10 relative to switch 12.

The switch 12 is shown as a sealed magnetic reed switch of the single pole double throw type. The switch includes a generally cylindrical elongated glass tube 18 sealed at its opposite ends to support and enclose parts of the switch mechanism. A pair of electrodes 20 and 22 formed of an electrically and magnetically conductive material are mounted at the right end of the tube 18. The electrodes 20 and 22 include respectively longitudinally extending spaced terminal parts 24 and 26 which are sealed to the tube 18 and project outside of the tube, and fixed contact parts 28 and 30 which are located within the tube in transversely spaced relation substantially centrally of the tube and which are more closely spaced than terminal parts 24 and 26. Electrode 20 is of integral one piece construction, while electrode 22 is of two part construction, having a permanent magnet 32 interposed between and welded to the terminal part 26 and the contact part 30. An electrically and magnetically conductive reed 34 is supported by the tube 18 at its opposite end and includes a terminal part 36 sealed to the tube and projecting outside of the tube, and a movable contact part 38 located within the tube and extending between contact parts 2 8.

The magnet 32 is magnetized such that it has north and south poles as designated by the letters N and S, and has a magnetic flux emanating therefrom which follows the path designated by the broken line A in FIGURE 1. This flux from magnet 32 traverses reed 34 and magnet 32 in the same direction and operates to attract the contact part 38 of reed 34 toward the. contact part 30 of the elecrode 22. Thus, contact part 38 of reed 34 forms a normally closed contact pair with contact part 30 of electrode 22 and forms a normally open contact pair with contact part 28 of electrode 20 as shown in FIGURE 1. The contact part 38 of reed 34 is moved from engagement with contact part 30 of electrode 22 to engagement with contact part 28 of electrode 20 when a magnetic field pro ducing means external of the tube 18 creates a field within the tube whose magnetic flux is oppositely directed with respect to magnetic flux A, as will hereinafter be further described. The sealed magnetic reed switch briefly described above is more particularly described and is claimed in U.S. Patent 3,117,202, assigned to the same assignee as the present invention. While a reed switch of this design is preferred in the present invention, other reed switch types may be employed.

Magnetic members 14 and 16 which are mounted on the shaft form a magnetic field producing means external of the tube 18 which creates a field within the tube whose magnetic flux is in certain predetermined positions of the shaft 10 oppositely directed with respect to magnetic flux A. The magnetic members 14 and 16 are preferably formed of permanent magnetic material which is magnetized to form field producing magnetic poles. Magnetic members 14 and 16, which are formed as disks having cylindrical peripheries 40 and 42 respectively, are magnetized so as to have one or more magnetic poles formed on the peripheries 40 and 42. As shown in FIGURES 1 and 2, the magnetic members 14 and 16 may each be magnetized along a single diameter so as to have diametrically opposed north and south poles as indicated by the letters N, S and N, S respectively, formed on the peripheries 40 and 42 respectively. In accordance with the normal convention, magnetic flux will emanate from the north poles and reenter at the south poles of the magnetic members 14 and 16.

Central bores coaxial with the cylindrical peripheries are provided in the magnetic members 14 and 16 to receive the shaft 10 such that they might be supported by the shaft in a side by side relationship as shown. The members 14 and 16 are adjustably secured to the shaft 10 by some suitable adjustable securing means such as collars 44 (only one of which is shown) which may be permanently secured to the magnetic members 14 and 16 and releasably secured to the shaft by the threaded fastening member 46.

The reed switch 12 is positioned adjacent the peripheries 40 and 42 of the magnetic members 14 and 16 with its axis perpendicular to the axis of the shaft and in the plane of the abutting faces of the magnetic members 14 and 16. It is further positioned with the shaft directly in line with the mating contact parts 28, 30 and 38, and with electrode 20 located closest to the magnetic members 14 and 16. While as set forth above, magnetic flux will emanate from the north pole of a magnetic member 14 and 16 and reenter its south pole, it will also emanate from the north pole of one of the magnetic members 14 and 16 and enter a south pole of the other magnetic member, should such a south pole be closer than its own south pole. Thus, except when the magnetic members 14 and 16 are secured to the shaft 10 with the N and S poles of member 14 in axial alignment with the N and S poles of member 16 respectively, magnetic flux will move from pole N to pole S and from pole N to pole S. The flux extending from pole N to pole S, is directed in a generally counter-clockwise direction about the shaft 10, while the flux extending from pole N to pole S is directed in a generally clockwise direction, as viewed in FIGURE 2.

The operation of the magnetically actuated limit switch will best be understood by further considering the path taken by flux extending from pole N to pole S when the shaft 10 is in the position shown in FIGURE 2, which position results from rotating the shaft in the direction of the arrow 48, i.e. clockwise, through approximately one-quarter of a revolution, i.e., ninety degrees from the position shown in FIGURE 1. This path, indicated by the broken line B, extends from pole N through the glass tube 18 to contact part 28, to spaced contact part 38, and back through the glass tube 18 to pole S on magnetic member 14. This flux exerts an attractive force between the contact part 28 of electrode 20 and the contact part 38 of reed 34 and the design is such that this force overcomes the attractive force created between contact parts 30 and 38 by permanent magnet 32 to disengage contact part 38 of reed 34 from contact part 30 of electrode 22 and to cause it to engage contact part 28 of electrode 20 as shown in FIGURE 2. Thus, as long as the path B taken by the flux between poles N and S includes contact parts 28 and 38, these contact parts will remain in engagement.

Referring to FIGURE 2, it is observed that the pole S on magnetic member 14 and the pole N on magnetic member 16 are angularly spaced 20: degrees, with the vertical diameter which passes through contact parts 28, 30 and 32 bisecting the angular space between them. With the magnetic poles N and S so spaced, the flux path B will continue to pass through and maintain contact parts 28 and 38 in engagement as the shaft is rotated clockwise or counter-clockwise approximately at degrees from the position shown. Rotation of the shaft clockwise or counter-clockwise from its position shown through an angle greater than 0: degrees but less than u-i-B degrees w-ill position two similar poles, i.e., N and N or S and S such that the vertical diameter which passes through contact parts 28, 30 and 32 will also pass through the space between such poles and therefore very little flux from magnetic members 14 and 16 will pass through the contact parts 28, 30 and 32 and contact part 38 will be attracted to contact part 30 by the flux from magnet 32 which follows the path A. Such a position being shown in FIGURE 1.

From the position shown in FIGURE 2, rotation of the shaft clockwise or counter-clockwise through an angle greater than 11-1- 3 degrees but less than 3+3a degrees will position poles S and N such that the vertical diameter passing through contact parts 28, 30 and 32 will also pass through the space between poles S and N, whereby the magnetic flux emanating from pole N and entering pole S will pass through the glass tube 18 to contact part 38 and engaged contact part 30, and back through the glass tube 18 to pole S, this path being indicated by the broken line C. Since this flux flows in a clockwise direction with respect to shaft 10, it is in the same direction as the flux from permanent magnet 32 which fiow in path A, and therefore strengthens the magnetic attraction between contact parts 38 and 30.

Thus it is seen that the limit switch functions as a rotational position indicator of shaft 10, by creating a closed circuit through electrode 20 and reed 34 for rotational positions within a degrees of that shown in FIGURE 2, and a closed circuit through electrode 22 and reed 34 for all other positions. By maintaining the positions of the magnetic members 14 and 16 relative to each other, but changing their positions relative to the shaft, the 20; degrees of rotation of shaft 10 during which a closed circuit is created through electrode 20 and reed 34 may be changed with respect to the shaft rotational position. By adjusting the angular positions of magnetic members 14 and 16 with respect to each other, such that poles S and N are either closer together or further apart, the number' of degrees represented by a is respectively decreased or increased. Moving poles S and N closer together will result in a closed circuit through electrode 20 and reed 34 for a narrower range of angular positions of the shaft 10. When poles S and N are brought into axial alignment the closed circuit through electrode 20 and reed 34 will not be formed, for magnetic flux path B is then perpendicular to the electrode 20 and reed 34 and is therefore ineffective to close the contact parts 28 and 38. The limit switch may also function as a shaft rotation counter sensor, in that continuous rotation of the shaft 10 in one direction will result in contact parts 28 and 38 and also contact parts 30 and 38 being engaged and disengaged once per revolution.

While one embodiment of a magnetically actuated limit switch assembly for detecting angular position and/or rotary motion of shaft 10 has been described, other embodiments of the invention will be apparent to those skilled in the art. For instance, the magnetic members 14 and 16 formed of a permanent magnetic material may be magnetized along more than one diameter so as to have two or more north and south poles on their cylindrical peripheries 40 and 42, respectively. In another instance, each of the magnetic members 14 and 16 might be magnetized with only one pole on its periphery, and with the other pole on the side facing the other magnetic member near the aperture at the center of the member. One of the members would be magnetized with a north pole on its periphery and the other with a south pole on its periphery such that the desired flux path B for actuation of the reed switch 12 is provided.

While a particular embodiment of this invention has been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects and, therefore, it is intended that the appended claims cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. A magnetically actuated limit switch for indicating relative movement or position of first and second objects comprising:

(a) a magnetically actuated switch supported from said first object having a fixed contact part and a movable contact part movable relative to said fixed contact part, said movable contact part being actuatable by a magnetic field;

(b) a first magnetic member having at least one pair of opposed wall surfaces, said first magnetic member further having at least one pair of unlike magnetic poles formed therein in substantially diametrically opposed relation relative to each other;

(c) first means supporting said first magnetic member from said second object;

((1) a second magnetic member having at least one pair of opposed wall surfaces, said second magnetic member further having at least one pair of unlike magnetic poles formed therein in substantially diametrically opposed relation relative to each other;

(e) second means supporting said second magnetic member from said second object with one of said pair of opposed wall surfaces of said second magnetic member in juxtaposed relation to one of said pair of opposed wall surfaces of said first magnetic member;

(f) at least one magnetic field extending between one of said pair of unlike magnetic poles on said first magnetic member and an unlike magnetic pole of said pair of unlike magnetic poles on said second magnetic member to actuate within a certain range of predetermined relative positions of said first and second objects said movable contact part of said magnetically actuated switch to indicate the relative movement or position of said first and second objects; and

(g) said movable contact part of said magnetically actuated switch being solely actuated by a magnetic field extending between unlike magnetic poles on said first and second magnetic members.

2. The magnetically actuated limit switch defined in claim 1 wherein said magnetically actuated switch is a magnetic reed switch and said movable contact part is a reed.

3. The magnetically actuated limit switch defined in claim 2 wherein said reed and said fixed contact part extend longitudinally in a sealed tube, and said one of said magnetic fields which actuates said reed extends over a path a portion of which extends longitudinally through said reed and said fixed contact part.

4. The magnetically actuated limit switch defined in claim 2 wherein said magnetic reed switch is a single pole double throw switch, having first and second spaced fixed contacts both of which are engageable by said reed.

.5. The magnetically actuated limit switch defined in claim 4 wherein a first one of said fixed contacts includes a permanent magnet, the magnetic flux of which traverses said reed and said first fixed contact to attract said reed to said first fixed contact to form a normally closed circuit, and wherein said one of said magnetic fields which actuates said reed traverses said reed and said second one of said fixed contacts in an opposite direction to the flux of said permanent magnet to cause said reed to disengage from said first fixed contact and to engage said second fixed contact to form a closed circuit therewith.

6. The magnetically actuated limit switch defined in claim 1 wherein said first means adjustably supports said first magnetic member from said second object such that the certain range of predetermined relative positions may be increased or decreased by increasing or decreasing the spacing between said unlike magnetic poles on said first and second magnetic members between which said one of said magnetic fields extends.

7. The magnetically actuated limit switch defined in claim 1 wherein said first means adjustably supports said first magnetic member from said second object and said second means adjustably supports said second magnetic member from said second object such that the certain range of predetermined relative positions may be adjusted to indicate different relative positions of said first and second objects.

8. A magnetically actuated limit switch indicating the angular position and/or rotary motion of a shaft comprising:

(a) a magnetically actuated switch positioned adjacent said shaft having a fixed contact part and a movable contact part movable relative to said fixed contact part, said movable contact part being actuatable by a magnetic field;

(b) a first magnetic member having at least one pair of opposed wall surfaces, said first magnetic member further having at least one pair of unlike magnetic poles formed therein in substantially diametrically opposed relation relative to each other;

(c) first means supporting said first magnetic member from said shaft;

((1) a second magnetic member having at least one pair of opposed wall surfaces, said second magnetic member further having at least one pair of unlike magnetic poles formed therein in substantially diametrically opposed relation relative to each other;

(e) second means supporting said second magnetic member from said shaft with one of said pair of opposed wall surfaces of said second magnetic member in juxtaposed relation to one of said pair of opposed wall surfaces of said first magnetic member;

(f) at least one magnetic field extending between one of said pair of unlike magnetic poles on said first magnetic member and an unlike magnetic pole of said pair of unlike magnetic poles on said second magnetic member to actuate within a certain range of predetermined relative rotative positions of said shaft said movable contact part of said magnetically actuated switch to indicate the relative rotative posi tion and/or rotary motion of said shaft; and

(g) said movable contact part of said magnetically actuated switch being solely actuated by a magnetic field extending between unlike magnetic poles on said first and second magnetic members.

'9. The magnetically actuated limit switch defined in claim 8 wherein said magnetically actuated switch is a magnetic reed switch and said movable contact part is a reed.

10. The magnetically actuated limit switch defined in claim 9 wherein said reed and said fixed contact part extend longitudinally in a sealed tube, and said one of said magnetic fields which actuates said reed extends over a path a portion of which extends longitudinally through said reed and said fixed contact part.

11. The magnetically actuated limit switch defined in claim 9 wherein said magnetic reed switch is a single pole double throw switch, having first and second spaced fixed contacts both of which are engageable by said reed.

12. The magnetically actuated limit switch defined in claim 11 wherein a first one of said fixed contacts includes a permanent magnet, the magnetic flux of which traverses said reed and said first fixed contact to attract said reed to said first fixed contact to form a normally closed circuit, and wherein said one of said magnetic fields which actuates said reed traverses said reed and said second one of said fixed contacts in an opposite direction to the flux of said permanent magnet to cause said reed to disengage from said first fixed contact and to engage said second fixed contact to form a closed circuit therewith.

13. The magnetically actuated limit switch defined in claim 8 wherein said first and second magnetic members are disks having cylindrical periphery of substantially the same diameters, at least one magnetic pole is formed on the periphery of each member, and at least one pole formed on the periphery of one of said members is of opposite polarity to at least one pole formed on the periphery of the other of said members, whereby at least one magnetic field extends around the peripheries of said members between opposite poles, one of which poles is on each of said members.

14. The magnetically actuated limit switch defined in claim 13 wherein said first and second magnetic members are each formed with a pair of opposite poles on their periphery, which poles are diametrically opposite each other on the peripheries.

15. The magnetically actuated limit switch defined in claim 13 wherein said disks are provided with a central bore coaxial with said cylindrical periphery and the shaft is received in said bores to support said disks in a side by side relationship.

16. The magnetically actuated limit switch defined in claim 8 wherein said first means adjustably supports said first magnetic member from said shaft that the certain range of predetermined relative positions may be increased or decreased by increasing or decreasing the spacing between said unlike magnetic poles on said first and second magnetic members between which said one of said magnetic fields extends.

17. The magnetically actuated limit switch defined in claim 8 wherein said first means adjustably supports said first magnetic member from said shaft and said second means adjustably supports said second magnetic member from said shaft such that the certain range of predetermined relative positions may be adjusted to indicate different relative positions of said shaft.

References Cited UNITED STATES PATENTS 2,999,914 9/1961 Stanaway 335-207 3,117,202 1/1964 Wertz 335153 3,133,173 5/1964 Vriens 335-153 X 3,233,060 2/1966 Wintriss 335-207 X BERNARD A. GILHEANY, Primary Examiner R. N. ENVALL, JR., Assistant Examiner 

